Countries with coastlines dumped around eight million tonnes of plastic waste in the world's oceans in 2010, scientists have estimated.
Double that amount is likely to be cast into the sea each year by 2025, generating a cumulative total in 10 years' time of 155 million tonnes, the experts predict.
China was said to be the worst offender, responsible for 27.7% of "mismanaged plastic" that found its way from the land to the ocean.
Other Asian countries, including Indonesia, the Philippines and Vietnam, were also at the top of a table of the 20 worst polluters compiled by the scientists.
The US was 20th on the list, accounting for 0.9% of the ocean-bound trash. The UK was not featured, but if 23 EU countries had been included they would collectively have ranked 18th, said the researchers.
Until now, it has been unclear how much plastic makes its way from the land to the sea.
The new estimates were obtained by combining known data on solid waste production from 192 different coastal countries with factors such as population density and economic status.
US lead researcher Dr Jenna Jambeck, from the University of Georgia, said: "Our estimate of eight million metric tons going into the oceans in 2010 is equivalent to five grocery bags filled with plastic for every foot of coastline in the world.
"This annual input increases each year, so our estimate for 2015 is about 9.1 metric tons.
"In 2025, the annual input would be about twice the 2010 input, or 10 bags full of plastic per foot of coastline."
The plastic waste assessed in the modelling study is generated by people living within 50 kilometres (31 miles) of the sea.
Previously, the extent of plastic pollution in the oceans has been monitored by counting fragments of the material hauled up in nets by survey ships.
These studies have revealed solid evidence of between 6,350 and 245,000 tonnes of plastic floating on the ocean surface - a much smaller amount than the quantity actually ending up in the sea, according to the new research.
Co-author Dr Kara Law, from the Sea Education Association, a US body that trains environmentalists, said: "This work gives us a sense of how much we're missing, how much we need to find in the ocean to add up to the total.
"There's a lot of plastic sitting on the bottom of the ocean and on beaches worldwide. Right now, we're mainly measuring plastic that floats, and only in relatively few locations."
The results appear in the journal Science and were also presented at the annual meeting of the American Association for the Advancement of Science (AAAS) taking place in San Jose, California.
Plastic waste encompasses an enormous range range of rubbish including bags, food wrappers, packaging, bottles, cups, toys and toothbrushes.
Experts are concerned about the amount ending up in the oceans because of the possible effect on wildlife and the environment. Plastic can entangle and trap ocean mammals such as whales, dolphins and seals, and is eaten by sea turtles, birds and fish.
Recent studies have shown that larger plastic fragments in the ocean can break down into tiny particles that can be ingested by small fish and crustaceans at the lower end of the food chain.
Waste plastic may leach out harmful persistent chemicals such as PCBs (polychlorinated biphenyls) that can spread through the food web, potentially ending up in humans.
